Wound Dressing Layer For Improved Fluid Removal

ABSTRACT

Disclosed herein are embodiments of a wound dressing layer. The wound dressing layer may include an open-cell foam. The foam may have a 50% compression force deflection of not more than about 4.8 kPa. The foam may also have a density of at least 24 kg/m3. The foam may exhibit a density increase of a factor of at least 12 at about −75 mmHg.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/473,169, filed Jun. 24, 2019, which is a U.S. National Stage Entry ofPCT/US2018/012212, filed Jan. 3, 2018, which claims the benefit, under35 USC § 119(e), of the filing of U.S. Provisional Patent ApplicationSer. No. 62/444,127, entitled “Wound Dressing Layer For Improved FluidRemoval,” filed Jan. 9, 2017. This provisional application isincorporated herein by reference for all purposes.

TECHNICAL FIELD

The present technology relates to wound dressing layers for applicationto a wound, to wound dressings including such a wound dressing layer, tosystems including such a wound dressing, and to methods related to thesame.

BACKGROUND

Clinical studies and practice have shown that reducing pressure inproximity to a tissue site can augment and accelerate growth of newtissue at the tissue site. The applications of this phenomenon arenumerous, but it has proven particularly advantageous for treatingwounds. Regardless of the etiology of a wound, whether trauma, surgery,or another cause, proper care of the wound is important to the outcome.Treatment of wounds or other tissue with reduced pressure may becommonly referred to as “negative-pressure therapy,” but is also knownby other names, including “negative-pressure wound therapy,”“reduced-pressure therapy,” “vacuum therapy,” “vacuum-assisted closure,”and “topical negative pressure,” for example. Negative-pressure therapymay provide a number of benefits, including migration of epithelial andsubcutaneous tissues, improved blood flow, and micro-deformation oftissue at a wound site. Together, these benefits can increasedevelopment of granulation tissue and reduce healing times.

While the clinical benefits of negative-pressure therapy are widelyknown, improvements to therapy systems, components, and processes maybenefit healthcare providers and patients.

BRIEF SUMMARY

Systems, apparatuses (for example, a wound dressing layer), and methodsfor using the same, for example, in a negative-pressure therapyenvironment, are set forth in the appended claims. Illustrativeembodiments are also provided to enable a person skilled in the art tomake and use the claimed subject matter.

For example, disclosed herein are embodiments of a wound dressing layer.The wound dressing layer may comprise an open-cell foam. The foam mayhave a 50% compression force deflection of not more than about 4.8 kPa.Also, the foam also has a density of at least 24 kg/m³. The foam mayexhibit a density increase of a factor of at least 12 at about −75 mmHg.

Also, disclosed herein are embodiments of a negative-pressure system forproviding negative-pressure therapy to a tissue site. The system maycomprise a wound dressing layer. The wound dressing layer may comprisean open-cell foam. The foam has a 50% compression force deflection ofnot more than about 4.8 kPa. Also, the foam may also have a density ofat least 24 kg/m³. The foam may exhibit a density increase of a factorof at least 12 at about −75 mmHg. Further, the system may comprise acover configured to be placed over the wound dressing layer. The covermay be sealed to tissue surrounding the tissue site to form a sealedspace. Further still, the system may comprise a negative-pressure sourceconfigured to be fluidly coupled to the sealed space.

Also disclosed herein are embodiments of a method for providingnegative-pressure therapy to a tissue site. The method may comprisepositioning a wound dressing layer proximate to the tissue site. Thewound dressing layer may comprise an open-cell foam. The foam may have a50% compression force deflection of not more than about 4.8 kPa. Also,the foam may also have a density of at least 24 kg/m³. The foam mayexhibit a density increase of a factor of at least 12 at about −75 mmHg.The method may also comprise placing a sealing member over the wounddressing layer and sealing the sealing member to tissue surrounding thetissue site to form a sealed space. The method may also comprise fluidlycoupling a negative-pressure source to the sealed space. The method mayalso comprise operating the negative-pressure source to draw fluid fromthe tissue site through the wound dressing layer and generate a negativepressure in the sealed space.

Objectives, advantages, and a preferred mode of making and using theclaimed subject matter may be understood best by reference to theaccompanying drawings in conjunction with the following detaileddescription of illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of an example embodiment of anegative-pressure therapy system including a wound dressing layer inaccordance with this specification.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The following description of example embodiments provides informationthat enables a person skilled in the art to make and use the subjectmatter set forth in the appended claims, but may omit certain detailsalready well-known in the art. The following detailed description is,therefore, to be taken as illustrative and not limiting.

The example embodiments may also be described herein with reference tospatial relationships between various elements or to the spatialorientation of various elements depicted in the attached drawings. Ingeneral, such relationships or orientation assume a frame of referenceconsistent with or relative to a patient in a position to receivetreatment. However, as should be recognized by those skilled in the art,this frame of reference is merely a descriptive expedient rather than astrict prescription.

Disclosed herein are embodiments of a dressing for example, a wounddressing comprising a wound dressing layer for improved fluid removal,referred to herein as a dressing layer. Also, disclosed herein areembodiments of a dressing including such a dressing layer, andnegative-pressure therapy systems including the same. Also disclosedherein are embodiments of methods related to the dressing layers, thedressings, and the negative-pressure therapy systems.

Referring to FIG. 1, an embodiment of a negative-pressure therapy system100 is shown in a simplified schematic. Generally, the negative-pressuretherapy system 100 may be configured to provide negative pressure to atissue site in accordance with the disclosure of this specification.

As used herein the term “tissue site” is intended to broadly refer to awound, defect, or other treatment target located on or within tissue,including but not limited to, bone tissue, adipose tissue, muscletissue, neural tissue, dermal tissue, vascular tissue, connectivetissue, cartilage, tendons, or ligaments. A wound may include chronic,acute, traumatic, subacute, and dehisced wounds, partial-thicknessburns, ulcers (such as diabetic, pressure, or venous insufficiencyulcers), flaps, and grafts, for example. The term “tissue site” may alsorefer to areas of any tissue that are not necessarily wounded ordefective, but are instead areas in which it may be desirable to add orpromote the growth of additional tissue.

In various embodiments, the negative-pressure therapy system generallyincludes a negative-pressure supply, and may include or be configured tobe coupled to a distribution component, such as a wound dressing. Ingeneral, a distribution component may refer to any complementary orancillary component configured to be fluidly coupled to anegative-pressure supply in a fluid path between a negative-pressuresupply and a tissue site. A distribution component may be detachableand, as well, may be disposable, reusable, or recyclable. For example,in the embodiment of FIG. 1, the negative-pressure therapy system 100includes a wound dressing 102 that is illustrative of a distributioncomponent fluidly coupled to a negative-pressure source 104.

As will be appreciated by the person of ordinary skill in the art uponviewing this disclosure, the fluid mechanics associated with using anegative-pressure source to reduce pressure in another component orlocation, such as within a sealed therapeutic environment, can bemathematically complex. However, the basic principles of fluid mechanicsapplicable to negative-pressure therapy are generally well-known tothose skilled in the art. Herein, the process of reducing pressure maybe described generally and illustratively herein as “delivering,”“distributing,” “providing,” or “generating” negative pressure, forexample.

In general, a fluid, such as wound fluid (for example, wound exudatesand other fluids), flow toward lower pressure along a fluid path. Thus,the term “downstream” typically implies something in a fluid pathrelatively closer to a source of negative pressure or further away froma source of positive pressure. Conversely, the term “upstream” impliessomething relatively further away from a source of negative pressure orcloser to a source of positive pressure. Similarly, it may be convenientto describe certain features in terms of fluid “inlet” or “outlet” insuch a frame of reference. This orientation is generally presumed forpurposes of describing various features and components herein. However,the fluid path may also be reversed in some applications (such as bysubstituting a positive-pressure source for a negative-pressure source)and this descriptive convention should not be construed as a limitingconvention.

As used herein, “negative pressure” is generally intended to refer to apressure less than a local ambient pressure, such as the ambientpressure in a local environment external to a sealed therapeuticenvironment provided by the wound dressing 102. In many cases, the localambient pressure may also be the atmospheric pressure proximate to orabout a tissue site. Alternatively, the pressure may be less than ahydrostatic pressure associated with the tissue at the tissue site.Unless otherwise indicated, values of pressure stated herein are gaugepressures. Similarly, references to increases in negative pressuretypically refer to a decrease in absolute pressure (e.g., a “morenegative” pressure), while decreases in negative pressure typicallyrefer to an increase in absolute pressure (e.g., a “less negative”pressure or a “more positive” pressure). While the amount and nature ofnegative pressure applied to a tissue site may vary according totherapeutic requirements, the pressure is generally a low vacuum, alsocommonly referred to as a rough vacuum, between −5 mm Hg (−667 Pa) and−500 mm Hg (−66.7 kPa). Common therapeutic ranges are between −75 mm Hg(−9.9 kPa) and −300 mm Hg (−39.9 kPa).

In various embodiments, a negative-pressure supply, such as thenegative-pressure source 104, may be a reservoir of air at a negativepressure, or may be a manual or electrically-powered device that canreduce the pressure in a sealed volume, such as a vacuum pump, a suctionpump, a wall suction port available at many healthcare facilities, or amicro-pump, for example. A negative-pressure supply may be housed withinor used in conjunction with other components, such as sensors,processing units, alarm indicators, memory, databases, software, displaydevices, or user interfaces that further facilitate therapy. Forexample, in some embodiments, the negative-pressure source may becombined with one or more other components into a therapy unit. Anegative-pressure supply may also have one or more supply portsconfigured to facilitate coupling and de-coupling of thenegative-pressure supply to one or more distribution components.

In the embodiment of FIG. 1, the negative-pressure therapy system 100includes a controller 110. The controller 110 may also be coupled to thenegative-pressure source 104. The controller 110 may generally beconfigured to control one or more operational parameters associated withthe negative-pressure therapy system. While in some embodiments anegative-pressure therapy system like the negative-pressure therapysystem 100 of FIG. 1 may include one or more sensors, for example, tomeasure operating parameters and provide feedback signals indicative ofthose operating parameters to a controller like the controller 110, inother embodiments, such sensors need not be included, as will bedisclosed herein. For example, in the embodiment of FIG. 1, thenegative-pressure therapy system 100 does not include any pressuresensor coupled a distribution component (such as the wound dressing 102)and to the controller 110 and configured to provide feedback to thecontroller 110, such as the pressure within the distribution component.In such an embodiment, the controller 110 may be characterized as an“open loop” controller. A controller, such as the controller 110, may bea microprocessor or computer programmed to operate one or morecomponents of the negative-pressure therapy system 100, such as thenegative-pressure source 104. In some embodiments, for example, thecontroller 110 may be a microcontroller, which generally comprises anintegrated circuit containing a processor core and a memory programmedto directly or indirectly control one or more operating parameters ofthe negative-pressure therapy system 100. Operating parameters mayinclude the power applied to the negative-pressure source 104, thepressure generated by the negative-pressure source 104, or the pressuredistributed to the dressing layer 108, for example. The controller 110may also be configured to receive one or more input signals, such as aninput signal from a user interface.

In some embodiments, the negative-pressure source 104 may be operativelycoupled to the wound dressing 102 via a dressing interface. In theembodiment of FIG. 1, the wound dressing 102 is coupled to thenegative-pressure source 104 such that the wound dressing 102 receivesnegative pressure from the negative-pressure source 104. In someembodiments, the negative-pressure therapy system 100 may include afluid container, such as a container 112, fluidly coupled to the wounddressing 102 and to the negative-pressure source 104. The container 112is representative of a container, canister, pouch, or other storagecomponent, which can be used to manage exudates and other fluidswithdrawn from a tissue site. In many environments, a rigid containermay be preferred or required for collecting, storing, and disposing offluids. In other environments, fluids may be properly disposed ofwithout rigid container storage, and a re-usable container could reducewaste and costs associated with negative-pressure therapy.

In various embodiments, components may be fluidly coupled to each otherto provide a path for transferring fluids (i.e., liquid and/or gas)between the components. For example, components may be fluidly coupledthrough a fluid conductor, such as a tube. As used herein, the term“tube” is intended to broadly include a tube, pipe, hose, conduit, orother structure with one or more lumina adapted to convey a fluidbetween two ends thereof. Typically, a tube is an elongated, cylindricalstructure with some flexibility, but the geometry and rigidity may vary.In some embodiments, two or more components may also be coupled byvirtue of physical proximity, being integral to a single structure, orbeing formed from the same piece of material. Moreover, some fluidconductors may be molded into or otherwise integrally combined withother components. Coupling may also include mechanical, thermal,electrical, or chemical coupling (such as a chemical bond) in somecontexts. For example, a tube may mechanically and fluidly couple thewound dressing 102 to the container 112 in some embodiments. In general,components of the negative-pressure therapy system 100 may be coupleddirectly or indirectly. For example, the negative-pressure source 104may be directly coupled to the controller 110, and may be indirectlycoupled to the wound dressing 102, for example, through the container112.

Wound Dressing

Often, in the context of negative-pressure therapy, negative pressuremay be applied to a tissue site (e.g., a wound) via materials anddevices generally characterized as “wound dressings.” Generally, inaddition to providing for the application of negative pressure to atissue site, wound dressings may control bleeding, ease pain, assist indebriding the wound, protect wound tissue from infection, modulateprotease activity, or otherwise promote healing and protect the woundfrom further damage. In some embodiments, a wound dressing may include acover, one or more layers configured to interface with the tissue site,or combinations thereof. For example, in the embodiment of FIG. 1, thewound dressing 102 includes a dressing layer 108 and a cover 106.

Wound Dressing—Cover

In various embodiments, the cover 106 may generally be configured toprovide a bacterial barrier and protection from physical trauma. Thecover 106 may also be constructed from a material that can reduceevaporative losses and provide a fluid seal between two components ortwo environments, such as between a therapeutic environment and a localexternal environment. The cover 106 may be, for example, an elastomericfilm or membrane that can provide a seal adequate to maintain a negativepressure at a tissue site for a given negative-pressure source. In someembodiments, the cover 106 may have a high moisture-vapor transmissionrate (MVTR), for example, for some applications. In such an embodiment,the MVTR may be at least 300 g/m² per twenty-four hours. In someembodiments, the cover 106 may be formed from a suitable polymer. Forexample, the cover 106 may comprise a polymer drape, such as apolyurethane film, that may be permeable to water vapor but generallyimpermeable to liquid. In such embodiments, the drape may have athickness in the range of about from 25 to about 50 microns. Inembodiments where the cover comprises a permeable material, the cover106 may have a permeability sufficiently low that a desired negativepressure may be maintained.

In some embodiments, the cover 106 may be configured to be attached toan attachment surface, such as undamaged epidermis, a gasket, or anothercover, for example, via an attachment device. For example, in theembodiment of FIG. 1, the cover is shown attached to epidermis so as toform a sealed space 107. In such an embodiment, the attachment devicemay take any suitable form. For example, an attachment device may be amedically-acceptable, pressure-sensitive adhesive that extends about aperiphery, a portion, or an entire sealing member. In some embodiments,for example, some or all of the cover 106 may be coated with an acrylicadhesive having a coating weight between 25-65 grams per square meter(g.s.m.). Thicker adhesives, or combinations of adhesives, may beapplied in some embodiments, for example, to improve the seal and reduceleaks. Other example embodiments of an attachment device may include adouble-sided tape, a paste, a hydrocolloid, a hydrogel, a silicone gel,or an organogel.

Wound Dressing—Dressing layer

In various embodiments, the dressing layer 108 may be generallyconfigured to distribute negative pressure, for example, so as tocollect fluid. For example, in some embodiments, the dressing layer 108may comprise or be configured as a manifold. A “manifold” in thiscontext generally includes any composition or structure providing aplurality of pathways configured to collect or distribute fluid across atissue site under pressure. For example, a manifold may be configured toreceive negative pressure from a negative-pressure source and todistribute negative pressure through multiple apertures (pores), whichmay have the effect of collecting fluid and drawing the fluid toward thenegative-pressure source. More particularly, in the embodiment of FIG.1, the dressing layer 108 is configured to receive negative pressurefrom the negative-pressure source 104 and to distribute the negativepressure through the dressing layer 108, for example, which may have theeffect of collecting fluid from the sealed space 107, for example, bydrawing fluid from the tissue site through the dressing layer 108. Inadditional or alternative embodiments, the fluid path(s) may be reversedor a secondary fluid path may be provided to facilitate movement offluid across a tissue site.

In some illustrative embodiments, the fluid pathways of a manifold maybe interconnected to improve distribution or collection of fluids. Insome embodiments, a manifold may be a porous foam material having aplurality of interconnected cells or pores. For example, cellular foams,open-cell foams, and reticulated foams generally include pores, edges,and/or walls adapted to form interconnected fluid pathways such as,channels. In various embodiments, foam-forming materials may be formedinto a foam, such as by curing, so as to include various apertures andfluid pathways. In some embodiments, a manifold may additionally oralternatively comprise projections that form interconnected fluidpathways. For example, a manifold may be molded to provide surfaceprojections that define interconnected fluid pathways.

In the embodiment of FIG. 1, the dressing layer 108 comprises orconsists essentially of a foam, for example, an open-cell foam, areticulated foam, or combinations thereof. In such an embodiment, theaverage pore size of such a foam may vary according to needs of aprescribed therapy. For example, in some embodiments, the dressing layer108 may be a foam having pore sizes in a range of 400-600 microns. Thetensile strength of the dressing layer 108 may also vary according toneeds of a prescribed therapy.

In various embodiments, the dressing layer 108 may be generallyconfigured to be in contact with the tissue site. For example, thedressing layer 108 may be in contact with a portion of the tissue site,substantially all of the tissue site, or the tissue site in itsentirety. If the tissue site is a wound, for example, the dressing layer108 may partially or completely fill the wound, or may be placed over(e.g., superior to) the wound. In various embodiments, the dressinglayer 108 may take many forms, and may have many sizes, shapes, orthicknesses depending on a variety of factors, such as the type oftreatment being implemented or the nature and size of a tissue site. Forexample, the size and shape of the dressing layer 108 may be adapted tothe contours of deep and irregular shaped tissue sites and/or may beconfigured so as to be adaptable to a given shape or contour. Moreover,in some embodiments, any or all of the surfaces of the dressing layer108 may comprise projections or an uneven, course, or jagged profilethat can, for example, induce strains and stresses on a tissue site, forexample, which may be effective to promote granulation at the tissuesite.

Foam materials may be characterized by an elastic modulus, which mayalso be referred to as a foam modulus. Generally, the elastic modulus ofa material, such as the dressing layer 108, may be a measure of theresistance of the material to elastic deformation under a load. Theelastic modulus of a material may be defined as the slope of astress-strain curve in the elastic deformation region of the curve. Theelastic deformation region of a stress-strain curve represents thatportion of the curve where deformation of a material due to an appliedload is elastic, that is, not permanent. If the load is removed, thematerial may return to its pre-loaded state. Generally, relatively“stiff” or “stiffer” materials may exhibit a relatively high elasticmodulus and, conversely, relatively more compliant materials may exhibita relatively low elastic modulus. Generally, a reference to the elasticmodulus of a material refers to a material under tension.

Similarly, for some materials under compression, the elastic modulus canbe compared between materials by comparing the compression forcedeflection of the respective materials. For instance, the compressionforce deflection may be determined experimentally by compressing asample of a material until the sample is reduced to about 25% of itsuncompressed size. Alternatively, the compression force deflection mayalso be measured by compressing a sample of a material to about 50% ofits uncompressed size. Generally, the load applied to the sample toreach the compressed state of the sample is then divided by the area ofthe sample over which the load is applied to yield the compression forcedeflection. The compression force deflection of a foam material can,inter alia, be a function of compression level, polymer stiffness, cellstructure, foam density, and cell pore size.

In some embodiments, the dressing layer 108 may be characterized as arelatively soft material. For example, in some embodiments, the dressinglayer 108 may have a 50% compression force deflection of not more thanabout 4.8 kPa, for example, from about 0.5 kPa to about 4.8 kPa or, in amore particular embodiment, from about 2.0 kPa to about 4.8 kPa. Thatis, the dressing layer 108 may exhibit compression of about 50% of itsuncompressed size if a load of not more than about 4.8 kPa is applied tothe dressing layer 108. Additionally, compression force deflection canrepresent the tendency of a foam to return to its uncompressed state ifa load is applied to compress the foam. For example, a dressing layer108 comprising or consisting essentially of foam and characterizedhaving a 50% compression force deflection of about 4.8 kPa may exertabout 4.8 kPa in reaction to 50% compression.

Further, foam materials, for example, the dressing layer 108, may becharacterized with respect to density. In some embodiments, the dressinglayer 108 may be characterized as a relatively dense material. Forexample, in various embodiments, the dressing layer 108 may have adensity of from about 24 kg/m³ to about 125 kg/m³ or, in a moreparticular embodiment, from about 24 kg/m³ to about 72 kg/m³.

Also, foam materials may be characterized as having a particular freevolume. In some embodiments, the dressing layer 108 may have a freevolume resulting from, for example, pores, channels, and othervoid-spaces within a foam material. For example, in various embodiments,a foam dressing layer 108 may be characterized as exhibiting a suitablefree volume, which may be calculated as the mass of the foam divided bythe density of the foam.

Foam materials may also be characterized by a particular porosity andpore size. The number of pores and the average pore size of the foam mayvary according to needs of a prescribed therapy. For example, in variousembodiments, a foam dressing layer 108 may be characterized asexhibiting a porosity of from about 20 pores per inch to about 120 poresper inch. Additionally, in various embodiments, a foam dressing layer108 may have an average pore size in a range of from about 400 to about600 microns.

Foam materials may also be characterized with respect to changes indensity upon the application of a compressive force. For example, asnoted herein, a foam may exhibit a particular compression forcedeflection (e.g., compression resultant from the application of a forceto the foam). More particularly, a foam embodiment of the dressing layer108 may be characterized as exhibiting a change in density responsive tothe application of a particular negative pressure, for example, anegative pressure effective to cause the ambient, atmospheric pressureto exert a compressing force with respect to a foam piece within asealed space to which the negative pressure is applied The densitychange may be observed by placing a foam a onto a flat surface, such asa sheet of plastic or metal, placing a flexible drape over the foam,connecting the interior space to a particular negative pressure, andmeasuring the thickness of foam at various applied negative pressures.For example, in some embodiments, the dressing layer 108 may becharacterized as exhibiting a density increase of a factor of at least 5(that is, the dressing layer 108 becomes five times more dense) at about−25 mmHg, a density increase of a factor of at least 9 at about −50mmHg, a density increase of a factor of at least 12 at about −75 mmHg, adensity increase of a factor of at least 14 at about −100 mmHg, adensity increase of a factor of at least 16 at about −125 mmHg, orcombinations thereof. For example, in some embodiments, the dressinglayer 108 may be characterized as exhibiting a density increase of afactor of at least 5 at about −25 mmHg, a density increase of a factorof at least 9 at about −50 mmHg, a density increase of a factor of atleast 12 at about −75 mmHg, a density increase of a factor of at least14 at about −100 mmHg, and a density increase of a factor of at least 16at about −125 mmHg.

In some embodiments, the dressing layer 108 may be hydrophobic. Forexample, the dressing layer 108 may be characterized as a hydrophobic,open-cell foam. Not intending to be bound by theory, in such anembodiment, the hydrophobic characteristics may prevent the foam fromdirectly absorbing fluid, such as wound exudate (e.g., from the tissuesite), but may allow the fluid to pass, for example, through theinternal structure. For example, in some embodiments, the foam may be ahydrophobic, open-cell polyurethane foam, a silicone foam, a polyetherblock amide foam, such as PEBAX®, an acrylic foam, a polyvinyl chloride(PVC) foam, a polyolefin foam, a polyester foam, a polyamide foam, athermoplastic elastomer (TPE) foam such as a thermoplastic vulcanizate(TPV) foam, and other crosslinking elastomeric foam such as foams formedfrom styrene-butadiene rubber (SBR) and ethylene propylene diene monomer(EPDM) rubber.

In an alternative embodiment, the dressing layer 108 may be hydrophilic.Not intending to be bound by theory, in such an embodiment, the dressinglayer 108 may be effective to wick fluid (e.g., away from the tissuesite), for example, while also continuing to distribute negativepressure to the tissue site. Not intending to be bound by theory, insuch an embodiment, the wicking properties of the dressing layer 108 maydraw fluid away from the tissue site by capillary flow or other wickingmechanisms. An example of a hydrophilic foam may include a polyvinylalcohol or polyether, open-cell foam. Other foams that may exhibithydrophilic characteristics include hydrophobic foams that have beentreated or coated to provide hydrophilicity. In one non-limitingexample, the dressing layer 108 may be a treated open-cell polyurethanefoam.

In various embodiments, the dressing layer 108 may be freeze dried, suchas through lyophilization.

Methods

In operation, for example, in the context of a negative-pressuretherapy, the dressing layer 108 may be placed within, over, on, orotherwise proximate to a tissue site, for example, a wound. The cover106 may be placed over the dressing layer 108 and the cover 106 sealedto an attachment surface near the tissue site. For example, the cover106 may be sealed to undamaged epidermis peripheral to a tissue site.Thus, the wound dressing 102, for example, the dressing layer 108 andthe cover 106, can provide a sealed therapeutic environment, forexample, a sealed space like sealed space 107, proximate to a tissuesite, substantially isolated from the external environment. Thenegative-pressure source 104 may be used to reduce the pressure in suchsealed therapeutic environment. For example, negative pressure appliedacross the tissue site, for example, via the dressing layer 108 caninduce macrostrain and microstrain in the tissue site, as well as removeexudates and other fluids from the tissue site, which can be collectedin container 112.

Advantages

The dressing layer, wound dressings including such a layer, andnegative-pressure therapy systems disclosed herein may providesignificant advantages, for example, when used in a negative-pressuretherapy, as also disclosed herein.

In some embodiments, the disclosed dressing layers, wound dressings, andsystems may be advantageously employed in the context ofnegative-pressure therapy, for example, to improve removal of woundfluid, such as wound exudate, for example, via the application ofnegative pressure. For example, a dressing layer of the type disclosedherein, for example, a foam dressing layer characterized as a relativelysoft material, characterized as relatively more dense, and/orcharacterized as exhibiting a relatively high density increase at aparticular negative pressure, may improve the quantity of fluid removedfrom a wound, the efficiency with which fluid is removed, or both. Forexample, and not intending to be bound by theory, fluid removal may bedependent upon the free volume within the foam and the compressibilityof the foam. For example, generally, a foam having a relatively higherdensity and characterized as relatively softer, for example, having arelatively higher compression force deflection and/or characterized asexhibiting a relatively high density increase, will have a lesser freevolume when compressed and, as such, will be more able to expel fluid.Referring to Table 1, below, the results of testing with regard toseveral foams varying as to density and/or pore size are shown:

Sample 1 Sample 2 Sample 3 Sample 4 (Granufoam) (45MC F3) (45MA F3)(45MA F5) Density 4.8 15 15 20 (kg/m³) Pore Size 400-600μ 120-200μ120-200μ 80-130μ (ppi) Saline 70 ml 60 ml 60 ml 55 ml Collected WetDressing 67.34 g 83.64 g 66.87 g 70.57 g Weight Fluid in 5.84 g 15.48 g16.06 g 21.03 g Dressing (g) Fluid in 5.89 ml 15.60 ml 16.19 ml 21.20 mlDressing (mL)

As shown in Table 1, the lowest-density foam yielded the highestquantity of fluid removal. The two foams having a density of 15 kg/m³yielded very similar quantities of fluid removal; these foams yieldedless fluid removal than the lowest-density foam, but more than thehighest-density foam. The highest-density foam yielded the lowestquantity of fluid removal. Again not intending to be bound by theory,the above-testing generally demonstrates that lower foam densities tendto yield improved fluid removal, potentially, because of thecorresponding stiffness of the more dense foams. More particularly, amore stiff foam may tend to oppose compression, for example, from theapplication of negative pressure, thereby allowing more fluid to remainin its pores. Also, a relatively low-density foam may have a relativelyhigh free volume in which fluid can accumulate. Finally, a relativelyhigh-density, low stiffness foam may tend to expel more fluid than acomparable foam with the same density but relatively higher stiffness,for example, in that the relatively stiffer foam is less able to becompress under a compressive force.

Thus, the dressing layers, the wound dressings including such a layer,and the negative-pressure therapy systems disclosed herein may allow forthe modulation of fluid removal for example, from a tissue site, such asa wound, even when utilizing a system that does not provide feedback,such negative-pressure feedback, to the negative-pressure source and/orcontroller. As such, the disclosed dressing layers, the wound dressingsincluding such a layer, and the negative-pressure therapy systems mayallow for improved fluid removal, for example, such that an open-loopfeedback system may be capable of achieving similar fluid removal to aclosed-loop system having feedback but employing a conventional wounddressing layer. As used herein, an “open-loop system,” which may also bereferred to as a non-feedback system, may refer to a system in which anoutput from the system has no influence or effect on the control actionof an input signal. For example, in an open-loop control system theoutput may not be “fed back” for purposes of altering the input. Also,as used herein, a “closed loop system,” which may also be referred to asa feedback system, may refer to a system having one or more feedbackloops between an output and an input. For example, in a closed-loopsystem some portion of the output may be returned “back” so as to alterthe input.

The term “about,” as used herein, is intended to refer to deviations ina numerical quantity that may result from various circumstances, forexample, through measuring or handling procedures in the real world;through inadvertent error in such procedures; through differences in themanufacture, source, or purity of compositions or reagents; fromcomputational or rounding procedures; and the like. Typically, the term“about” refers to deviations that are greater or lesser than a statedvalue or range of values by 1/10 of the stated value(s), e.g., ±10%. Forinstance, a concentration value of “about 30%” refers to a concentrationbetween 27% and 33%. Each value or range of values preceded by the term“about” is also intended to encompass the embodiment of the statedabsolute value or range of values. Whether or not modified by the term“about,” quantitative values recited in the claims include equivalentsto the recited values, for example, deviations from the numericalquantity, but would be recognized as equivalent by a person skilled inthe art.

The appended claims set forth novel and inventive aspects of the subjectmatter disclosed and described above, but the claims may also encompassadditional subject matter not specifically recited in detail. Forexample, certain features, elements, or aspects may be omitted from theclaims if not necessary to distinguish the novel and inventive featuresfrom what is already known to a person having ordinary skill in the art.Features, elements, and aspects described herein may also be combined orreplaced by alternative features serving the same, equivalent, orsimilar purpose without departing from the scope of the inventiondefined by the appended claims.

What is claimed is:
 1. A negative-pressure wound therapy system,comprising: a wound dressing, the wound dressing comprising an open-cellfoam having a 50% compression force deflection of not more than about4.8 kPa, a density of at leas 24 kg/m³, and exhibiting a densityincrease of a factor of at least 12 at about −75 mmHg; wherein the wounddressing is configured to be disposed under a cover, the coverconfigured to be attached to tissue surrounding a tissue site; andwherein the wound dressing is configured to be fluidly coupled to anegative-pressure source.
 2. The negative-pressure wound therapy systemof claim 1, wherein the wound dressing has a 50% compression forcedeflection of not more than about 4.5 kPa.
 3. The negative-pressurewound therapy system of claim 1, wherein the wound dressing has a 50%compression force deflection of not more than about 4.0 kPa.
 4. Thenegative-pressure wound therapy system of claim 1, wherein the wounddressing has a 50% compression force deflection of not more than about3.5 kPa.
 5. The negative-pressure wound therapy system of claim 1,wherein the wound dressing has a 50% compression force deflection of notmore than about 3.0 kPa.
 6. The negative-pressure wound therapy systemof claim 1, wherein the wound dressing has a density of at least 28kg/m³.
 7. The negative-pressure wound therapy system of claim 1, whereinthe wound dressing has a density of at least 32 kg/m³.
 8. Thenegative-pressure wound therapy system of claim 1, wherein the wounddressing has a density of at least 36 kg/m³.
 9. The negative-pressurewound therapy system of claim 1, wherein the wound dressing has adensity of at least 40 kg/m³.
 10. The negative-pressure wound therapysystem of claim 1, wherein the wound dressing exhibits a densityincrease of a factor of at least 5 at about −25 mmHg.
 11. Thenegative-pressure wound therapy system of claim 1, wherein the wounddressing exhibits a density increase of a factor of at least 9 at about−50 mmHg.
 12. The negative-pressure wound therapy system of claim 1,wherein the wound dressing exhibits a density increase of a factor of atleast 14 at about −100 mmHg.
 13. The negative-pressure wound therapysystem of claim 1, wherein the wound dressing exhibits a densityincrease of a factor of at least 16 at about −125 mmHg.
 14. Thenegative-pressure wound therapy system of claim 1, wherein the wounddressing is hydrophobic.
 15. The negative-pressure wound therapy systemof claim 1, wherein the open-cell foam is formed from polyurethane.